1. Field of the Invention
The present invention relates to wireless, chip-to-chip communications adapted for transferring data for integrated circuits mounted within a support structure like a chassis or a printed circuit board; and more particularly to so-called impulse radio or ultra-wideband (UWB) radio channels adapted for such use.
2. Description of Related Art
UWB radio systems have been proposed for wireless chip-to-chip communications systems. One example technique for such use is pulse position modulation (PPM) for communication of data. Unlike the typical narrowband radio systems which require heterodyne receiver architectures, a UWB radio system requires a simpler “correlator” circuit which consumes less power and less circuit area, and can be integrated with standard bulk CMOS processes. For reference, see N. Daniele, et al., “Principle and Motivations of UWB Technology for High Data Rate WPAN Applications,” Smart Objects Conference, May 15-17, 2003, Grenoble, France; and Win, et al., “Impulse Radio: How It Works,” IEEE Communications Letters, Vol. 2, No. 2, February, 1998.
Also, as described by Daniele, et al., unlike narrowband systems, the theoretical channel capacity of a UWB system increases exponentially as the distance between transmitter and receiver is reduced. According to this characteristic multi-channel, multi-gigabit-per-second Gbps signaling over the distance of a few centimeters is possible.
However, a significant drawback for UWB systems, compared with sinusoidal radio systems, is the requirement of a precise timing source at both the transmitter and the receiver. This requirement can be understood in the context of a PPM system by considering that to distinguish between a transmitted “0” and a transmitted “1,” a UWB receiver needs to be able to distinguish the position of a received Gaussian mono-cycle pulse with accuracy on the order of less than 100 picoseconds in a representative embodiment.
Some of the basic principles of pulse position modulation are also described by Daniele, et al. In a PPM scheme, a transmitted pulse is transmitted during a given timing slot from a transmitter, and is received at a receiver after a nominal pulse interval NPI, corresponding with the time of flight of the transmitted pulse from the transmitter to the receiver. The signal is modulated to indicate a logic “0” and a logic “1” by transmitting either early or late. Thus, a logic “0” is received early with respect to the NPI at the receiver, and a logic “1” is received late. The amount of the shift in time between the early and late pulses is very small, such as on the order of 100 picoseconds in some systems.
A typical process of receiving the transmitted PPM pulse is also described in Daniele, et al. Logic “0” and logic “1” PPM modulation positions are shifted in phase from a nominal sample time. The received signals are combined with a correlation pattern aligned with the nominal sample time, and in some systems integrated over a number of samples, to produce a detector output. For example, one correlation pattern described in the Daniele, et al. article is set up so that if the received pulse is a logic “0,” then the result of multiplication with the correlation pattern will be positive. On the other hand, if the received pulse is a logic “1,” then the result of multiplication with the correlation pattern will be negative. As can be appreciated, if the correlation pattern is misaligned with respect to the nominal sample time, the correlation with early and late pulses becomes distorted, and significant receiver error will occur. This makes UWB systems highly sensitive to timing imperfections, which are difficult to overcome in low-cost systems.
It is desirable to provide techniques for chip-to-chip communication using UWB and other wireless technologies, which provide more efficient utilization of system resources, and overcome the problems of timing imperfections encountered in the prior art.